Radio employing a self calibrating transmitter with reuse of receiver circuitry

ABSTRACT

A radio includes a self-calibrating transmitter that uses a portion of a receiver section to perform self-calibration. Accordingly, the radio includes a transmitter section, mixer, analog receiver section, calibration switch module, digital receiver section, calibration determination module, and calibration execution module. The transmitter section produces a modulated RF signal from base-band signal and a transmitter local oscillation. The mixer mixes the modulated RF signal with the transmitter local oscillation to produce a base-band representation of the modulated RF signal. In calibration mode, the calibration switch module provides the base-band representation to the receiver section, which processes the representation to produce a 2 nd  base-band digital signal. The calibration determination module interprets frequency components of the 2 nd  base-band digital signal to produce a calibration signal that compensates for imbalances within the transmitter.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to communication systems and moreparticularly to radio transceivers used within such communicationsystems.

BACKGROUND OF THE INVENTION

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), and/or variations thereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, et cetera communicates directlyor indirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel (e.g., one of the plurality of radiofrequency (RF) carriers of the wireless communication system) and shareinformation over that channel. For indirect wireless communications,each wireless communication device communicates directly with anassociated base station (e.g., for cellular services) and/or anassociated access point (e.g., for an in-home or in-building wirelessnetwork) via an assigned channel. To complete a communication sessionbetween the wireless communication devices, the associated base stationsand/or associated access points communicate with each other directly,via a system controller, via the public switch telephone network, viathe internet, and/or via some other wide area network.

For each wireless communication device to participate in wirelesscommunications, it includes a built-in radio transceiver (i.e., receiverand transmitter) or is coupled to an associated radio transceiver (e.g.,a station for in-home and/or in-building wireless communicationnetworks, RF modem, etc.). As is known, the receiver receives RFsignals, removes the RF carrier frequency from the RF signals directlyor via one or more intermediate frequency stages, and demodulates thesignals in accordance with a particular wireless communication standardto recapture the transmitted data. The transmitter converts data into RFsignals by modulating the data in accordance with the particularwireless communication standard and adds an RF carrier to the modulateddata in one or more intermediate frequency stages to produce the RFsignals.

As the demand for enhanced performance (e.g., reduced interferenceand/or noise, image rejection, improved quality of service, compliancewith multiple standards, increased broadband applications, et cetera),smaller sizes, lower power consumption, and reduced costs increases,wireless communication device engineers are faced with a very difficultdesign challenge to develop such a wireless communication device.Typically, an engineer is forced to compromise one or more of thesedemands to adequately meet the others. For instance, an engineer maychoose a direct conversion topology (i.e., convert directly from an RFsignal to a base-band signal or directly from a base-band signal to anRF signal) to meet size requirements and/or broadband applicationrequirements. However, for direct conversion transceivers, noise and/orinterference increases due to local oscillation leakage, imagingproblems, non-linearities due to component mismatches and/or processvariations are more detrimental to overall performance are morepronounced.

As is known, local oscillation leakage results from I-Q DC offset andimperfections of the mixers within a transmitter that allow the localoscillation, which equals the RF, to be present in the resultant RFsignal. The local oscillation leakage can be minimized by using multipleIF stages within the transmitter. In such an implementation, each IFstage uses a local oscillation that has a significantly differentfrequency than the RF, with the sum of the multiple local oscillationsequals the RF. Since each local oscillation has a significantlydifferent frequency than the RF, each local oscillation is outside theRF band of interest (i.e., the frequency spectrum of the resulting RFsignal). But this requires an abandoning of the direct conversiontopology and its benefits with respect to size reduction, powerconsumption reduction, reduced costs, and reduced complexity forbroadband applications.

Therefore, a need exists for a low power, reduced size, reduced cost,and robust performance direct conversion topology radio, radiotransmitter, radio receiver, and/or components thereof.

SUMMARY OF THE INVENTION

These needs and others are substantially met by the radio having aself-calibrating transmitter. The radio includes a transmitter section,mixer, analog receiver section, calibration switch module, digitalreceiver section, calibration determination module, and calibrationexecution module. The transmitter section produces a modulated radiofrequency (RF) signal based on an I-component and Q-component of abase-band signal and an I-component and Q-component of a transmitterlocal oscillation.

The mixer is operably coupled to mix the modulated RF signal with an Ior Q component of the transmitter local oscillation to produce abase-band representation of the modulated RF signal.

The calibration switch module is operably coupled to the analog receiversection and the digital receiver section. When the radio is in normalmode, the calibration switch module outputs analog low IF signals, whichare produced by the analog receiver section, to the digital receiversection for recapturing the embedded data. During calibration mode, thecalibration switch module provides the base-band representation of themodulated RF signal to the digital receiver section.

In calibration mode, the digital receiver section produces a 2^(nd)base-band digital signal from the base-band representation of themodulated RF signal. The calibration determination module interprets the2^(nd) base-band digital signal to produce a calibration signal. Such adetermination is based on analyzing the frequency spectrum of the 2^(nd)base-band digital signal to determine local oscillation leakage andimbalances within the transmitter. Accordingly, the calibration signalis generated to minimize local oscillation leakage and/or imbalanceswithin the transmitter.

The calibration execution module is operably coupled to calibrate the DClevel of the I and/or Q component of the base-band signal and/or thegain of the I and Q component of the base-band signal in accordance withthe calibration signal to reduce imbalances within the transmittersection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a communication systemthat includes wireless communication devices in accordance with thepresent invention;

FIG. 2 illustrates a schematic block diagram of a wireless communicationdevice in accordance with the present invention;

FIG. 3 illustrates a schematic block diagram of a self-calibratingtransmitter in accordance with the present invention;

FIG. 4 illustrates a schematic block diagram of the calibrationdetermination module and calibration execution module in accordance withthe present invention;

FIG. 5 illustrates a graphical representation of the frequency spectrumfor a base-band representation of a modulated RF signal when performinga DC offset calibration in accordance with the present invention;

FIG. 6 illustrates a graphical representation of the frequency spectrumfor a base-band representation of a modulated RF signal when performinga gain offset calibration in accordance with the present invention;

FIG. 7 illustrates a logic diagram of a method for generating acalibration signal to minimize DC offset levels within theself-calibrating transmitter in accordance with the present invention;

FIG. 8 illustrates a logic diagram of a method for generating acalibration signal to optimize gain within a self-calibratingtransmitter in accordance with the present invention;

FIG. 9 illustrates a schematic block diagram of an alternateself-calibrating transmitter in accordance with the present invention;

FIG. 10 illustrates a logic diagram of a method for self-calibrating atransmitter in accordance with the present invention;

FIG. 11 illustrates an alternate schematic block diagram of a radio inaccordance with the present invention;

FIG. 12 illustrates a schematic block diagram of calibration circuitrywithin the radio of FIG. 11;

FIG. 13 illustrates a schematic block diagram of an alternate radio inaccordance with the present invention; and

FIG. 14 illustrates a logic diagram for transceiving signals utilizing aself-calibrating transmitter in accordance with the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a schematic block diagram of a communication system10 that includes a plurality of base stations and/or access points12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 2.

The base stations or access points 12 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12-16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its area. Typically, thewireless communication devices register with a particular base stationor access point 12-14 to receive services from the communication system10. For direct connections (i.e., point-to-point communications),wireless communication devices communicate directly via an allocatedchannel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. The radio includes aself-calibrating direct conversion transmitter as disclosed herein toenhance performance, reduce costs, reduce size, and/or enhance broadbandapplications.

FIG. 2 illustrates a schematic block diagram of a wireless communicationdevice that includes the host device 18-32 and an associated radio 60.For cellular telephone hosts, the radio 60 is a built-in component. Forpersonal digital assistants hosts, laptop hosts, and/or personalcomputer hosts, the radio 60 may be built-in or an externally coupledcomponent.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides outbound data from theprocessing module 50 to the radio 60. The processing module 50 mayreceive the outbound data from an input device such as a keyboard,keypad, microphone, et cetera via the input interface 58 or generate thedata itself For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, a receiver section, a transmittersection, local oscillation module 74, and an antenna 86. The receiversection includes a digital receiver processing module 64,analog-to-digital converter 66, filtering/gain module 68, downconversion module 70, low noise amplifier 72, and at least a portion ofmemory 75. The transmitter section includes a digital transmitterprocessing module 76, digital-to-analog converter 78, filtering/gainmodule 80, up-conversion module 82, power amplifier 84, and at least aportion of memory 75. The antenna 86 may be a single antenna that isshared by the transmit and receive paths or may include separateantennas for the transmit path and receive path. The antennaimplementation will depend on the particular standard to which thewireless communication device is compliant.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, constellation mapping, modulation,and/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry. The memory 75stores, and the processing module 64 and/or 76 executes, operationalinstructions corresponding to at least some of the functions illustratedin FIGS. 3-14.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE802.11a, IEEE802.11b, Bluetooth, etcetera) to produce digital transmission formatted data 96. The digitaltransmission formatted data 96 will be a digital base-band signal or adigital low IF signal, where the low IF will be in the frequency rangeof zero to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogsignal prior to providing it to the up-conversion module 82. Theup-conversion module 82 directly converts the analog baseband or low IFsignal into an RF signal based on a transmitter local oscillationprovided by local oscillation module 74. The power amplifier 84amplifies the RF signal to produce outbound RF signal 98. The antenna 86transmits the outbound RF signal 98 to a targeted device such as a basestation, an access point and/or another wireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the low noise amplifier 72, which amplifies the signal 88to produce an amplified inbound RF signal. The low noise amplifier 72provide the amplified inbound RF signal to the down conversion module70, which directly converts the amplified inbound RF signal into aninbound low IF signal based on a receiver local oscillation provided bylocal oscillation module 74. The down conversion module 70 provides theinbound low IF signal to the filtering/gain module 68, which filtersand/or adjusts the gain of the signal before providing it to the analogto digital converter 66.

The analog-to-digital converter 66 converts the filtered inbound low IFsignal from the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

FIG. 3 illustrates a schematic block diagram a self-calibratingtransmitter 100 that may be incorporated into radio 60. Theself-calibrating transmitter 100 includes the digital transmitterprocessing module 76, the digital-to-analog converter 78, thefiltering/gain module 80, the up-conversion module 82 and the poweramplifier 84. In an IEEE 802.11a compliant embodiment, the digitaltransmitter processing module 76 is configured to produce a scrambleand/or encode module 101, and a modulation mapping module 103. For anyembodiment of the self-calibrating transmitter (i.e., transmitterembodiments that are compliant with various ones of the plurality ofwireless communication standards) is further configured to include acalibration execution module 102 and a portion of the calibrationdetermination module 104. The up-conversion module 82 includes a 1^(st)mixer 106, a 2^(nd) mixer 108 and a summing module 110.

To implement the self-calibrating function, the self-calibratingtransmitter 100 places itself in a calibration mode. During calibrationmode, the digital transmitter processing module 76 receives asquare-wave signal as the outbound data 94. The scramble/encode module101 of the digital processing module 76 scrambles and/or encodes thesquare-wave signal and provides the scrambled and/or encoded signal tothe modulation mapping module 103. The modulation mapping module 103maps the scrambled and/or encoded signal to a constellation symbol,which includes an I component and a Q component. In the illustration ofFIG. 3, the constellation symbol is designated as the digitaltransmission formatted data 96.

The digital-to-analog converter 78 converts the I and Q components ofthe digital transmission formatted data 96 (i.e., the encoded andconstellation mapped calibration signal) into an analog I component ofthe calibration signal and an analog Q component of the calibrationsignal. The filtering/gain module 80 filters and/or adjusts the gain ofthe analog I component and/or the analog Q component of the calibrationsignal to produce an I component and a Q component of a baseband signal117.

The up-conversion module 82 receives the I and Q components of thebaseband signal 117 and mixes them with the I and Q components of thelocal oscillation 74 and sums the mixed signals to produce the modulatedRF signal 112. In particular, the 1^(st) mixer 106 mixes an I componentof the base-band signal 117 with an I component of the local oscillation74 to produce a first mixed signal. The 2^(nd) mixer 108 mixes a Qcomponent of the base-band calibration signal 117 with a Q component ofthe local oscillation 74 to produce a second mixed signal. Summingmodule 110 sums the resulting mixed signals to produce the modulated RFcalibration signal 112.

The calibration determination module 104 receives the modulated RFsignal 112 and the I or Q component of the local oscillation 74. Basedon these inputs, the calibration determination module 104 determines DCoffset within the transmitter and may further determine gain imbalanceswithin the transmitter. In general, the calibration determination module104 produces baseband representation of the modulated RF signal 112 fromthe local oscillation and the modulated RF signal 112. The calibrationdetermination module 104 then filters the baseband representation of themodulated RF signal 112 to isolate frequency spectrum components. Next,the calibration determination module 104 interprets the frequencyspectrum components with respect to anticipated frequency spectrumcomponents that are derived based on the known input signal and anassumption that the transmitter has no DC offsets and no gain imbalancesto determine DC offset and/or gain imbalances of the I and/or Q paths ofthe transmitter. Based on the interpretation, the calibrationdetermination module 104 generates a calibration signal 116 tocompensate for DC offsets and/or gain imbalances.

The calibration determination module 104 provides the calibration signal116 to the calibration execution module 102, which adjusts the DC offsetand/or gain of the I and/or Q component of the digital transmissionformatted data 96 in accordance with the calibration signal 116. Havingmade this adjustment, the calibration mode may be repeated to optimizethe calibration signal or concluded, returning the transmitter to normaloperation. In normal operation (e.g., in compliance with IEEE 802.11a)the scramble/encoder module 101 scrambles and/or encodes the outbounddata 94 received from the host device to produce encoded data. Themodulation mapping module 103 maps the encoded data to constellationsymbols to produce I and Q components of non-calibrated digitaltransmission formatted data. The calibration execution module 102adjusts the DC offset and/or gain of the I and/or Q component of thenon-calibrated digital transmission formatted data based on thecalibration signal to produce the digital transmission formatted data96. The digital-to-analog converter 78, filtering gain module 80 andup-conversion module 82 operate to produce an RF signal representing thedigital transmission formatted data 96. The power amplifier 84 amplifiesthe RF signal to produce outbound RF signal 98.

FIG. 4 illustrates a schematic block diagram of the calibrationdetermination module 104 and calibration execution module 102 of theself-calibrating transmitter of FIG. 3. The calibration determinationmodule 104 includes a down-converting mixing module 120, adigital-to-analog converter 122, a filtering module 124, and aninterpreting module 126. The filtering module 124 and interpretingmodule 126 are implemented in the digital transmitter processing module76. As shown, the filtering module 124 may include a low-passfilter/band-pass filter 128 and a band-pass filter 130. The calibrationexecution module 102 includes a 1^(st) gain offset module 138, a 1^(st)DC offset module 140, a 2^(nd) gain offset module 142, and a 2^(nd) DCoffset module 144.

To establish the calibration signal 116 for each of the modules 138-144of the calibration execution module 102, the calibration determinationmodule 104 separately tests the transmitter 100 for DC offset and gainimbalances. To test for DC offset, the filter module 124 receivescoefficients for the LPF/BPF module 128 such that it functions as a lowpass filter.

In DC offset calibration mode, the down-converting mixing module 120mixes the modulated RF signal 112 with the I component of the localoscillation to produce a base-band representation 121 of the modulatedRF signal 112. The digital-to-analog converter 122 converts thebase-band representation 121 into a digital base-band signal 132. Thelow-pass/band-pass filter 128 passes a 1^(st) frequency spectrumcomponent 134 of the digital baseband signal 132 (which represents thecarrier leakage at DC) to the interpreting module 126. The band-passfilter 130 passes a 2^(nd) frequency spectrum component 136 of thedigital base-band signal 132 (which represents the desired transmittedsignal) to the interpreting module 126.

Referring simultaneously to FIGS. 4 and 5, FIG. 5 illustrates thefrequency spectrum of the digital baseband signal 132, which has a sinX/X waveform, and the corresponding filtering of the filter module 124.The low pass filtering of LPF 128 isolates the transmitted signalcomponent at DC of the digital baseband signal 132 plus any DC offset,which is represented by LO leakage 150. The bandpass filtering of BPF130 isolates the desired transmitted signal at a known samplingfrequency point.

The filtering module 124 provides the 1^(st) frequency spectrumcomponent (i.e., the transmitted signal component at DC of the digitalbaseband signal 132 plus any DC offset) and the 2^(nd) frequencyspectrum component (i.e., the desired transmitted signal at the knownsampling point) to the interpreting module 126. The interpreting module126 interprets the 1^(st) and 2^(nd) frequency spectrum components 134and 136 with respect to each other and with respect to known propertiesof the digital baseband signal 132 (i.e., in the frequency domain it isa sin X/X waveform) to determine the LO leakage component 150.

As one of average skill in the art will appreciate, there is a varietyof ways in which the interpreting module 126 may interpret the 1^(st)and 2^(nd) frequency spectrum components to produce the calibrationsignal. For instance, the 1^(st) and/or 2^(nd) frequency spectrumcomponents are compared with each other. If they do not sufficientmatch, (e.g., the difference is less than a threshold value), theinterpreting module 126 generates the calibration signal 116 to correctfor DC offset.

Alternatively, the interpreting module 126 may calculate an ideal 1^(st)frequency spectrum component based on the 2^(nd) frequency spectrumcomponent 136 and known properties of the digital baseband signal 132(i.e., that it is a sin X/X waveform). The interpreting module 126compares the ideal 1^(st) frequency spectrum component with the actual1^(st) frequency spectrum component to determine the LO leakage 150.Having determined the LO leakage, the interpreting module 126 generatesthe calibration signal to adjust the DC level of the I and/or Q paths ofthe transmitter via DC offset module 140 and/or DC offset module 144,respectively.

DC offset module 140 and/or 144, which, in one embodiment, may besumming modules, receives the calibration signal 116, which represents aDC offset adjustment voltage, and either adds or subtracts the DC offsetadjustment voltage to/from its corresponding input. If both DC offsetmodules 140 and 144 are to offset their respective inputs, thecalibration signal 116 includes a DC offset adjust voltage for DC offsetmodule 140 and another one for DC offset module 144. At this point, theprocess may be repeated to further optimize the calibration signal 116.

In a gain offset calibration mode, the calibration determination module104 is determining gain imbalances between the I path and the Q path ofthe transmitter. To do this, a calibration signal is provided to thetransmitter such that a modulated RF signal 112 is produced for thecalibration signal. The down-converting mixing module 120 mixes themodulated RF calibration signal 112 with the I component of the localoscillation to produce a base-band representation 121 of the RFcalibration signal 112. The digital-to-analog converter 122 converts thebase-band representation 121 into a digital base-band signal 132.

The filtering module 124 receives filtering coefficients that configurethe low-pass filter/band-pass filter 128 to function as a band-passfilter centered at a particular frequency and centers the band-passfilter 130 at a complimentary frequency as shown in FIG. 6. Theband-pass filter 128 filters the digital base-band signal 132 to producea 1^(st) frequency spectrum component 134 while band-pass filter 130filters the digital base-band signal 132 to produce a 2^(nd) frequencyspectrum component 136. The interpreting module 128 interprets the1^(st) and 2^(nd) frequency spectrum components 134 and 136 to determinean imbalance. If an imbalance exists, i.e., the magnitudes of the 1^(st)and 2^(nd) frequency spectrum components 134 and 136 do not sufficientlymatch (e.g., greater than a pre-stored threshold) the interpretingmodule 126 generates the calibration signal 116 to compensate for theimbalance.

The interpreting module 126 provides the calibration signal 116 to gainoffset module 138 and/or gain offset module 142, which adjusts the gainof the I and/or Q path in accordance with the calibration signal 116. Inone embodiment, the gain offset modules 138 and 142 include multipliersthat multiple a gain offset value indicated by the calibration signal116 with a corresponding input signal. As such, the calibration signalis reflective of the amount of gain offset and may be a value that isless than, equal to, or greater than one.

FIG. 7 illustrates a logic diagram of a method performed by thecalibration determination module to establish the calibration signal toadjust the DC offset. The process begins at Step 160 where 1^(st) and2^(nd) sets of coefficients are provided to the filtering module toproduce a low-pass filter and a band-pass filter. The process thenproceeds to Step 162 where the DC level of the I and/or Q components ofthe base-band signal are adjusted in accordance with the DC offsetcorrection indication, which is indicated by the calibration signal.

The process then proceeds to Step 164 where a new 1^(st) frequencyspectrum component and a new 2^(nd) frequency spectrum components areproduced based on the adjusted I and/or adjusted Q components of thebase-band signal. The process then proceeds to Step 168 where thecalibration determination module determines whether the new 1^(st)frequency spectrum component represents less transmitter DC offset thanthat represented by the 1^(st) frequency spectrum. If so, the processproceeds to Step 170 where the calibration determination module producesan updated calibration signal to fine-tune the DC offset level of the Iand/or Q components of the base-band signal.

Having updated the calibration signal, the calibration determinationmodule determines whether the DC offset level has reached an optimalpoint. If so, the process is complete. If not, the process proceeds toStep 174 where the calibration determination module produces updatedfrequency spectrum components by tweaking the calibrating signal andrepeating the calibration. The process then reverts to Step 170 andremains in this loop until an optimal DC offset level is reached.

If, at Step 166, the new frequency spectrum components do not representless transmitter DC offset than the previous frequency spectrumcomponents, the process proceeds to Step 168. At Step 168, thecalibration determination module produces an updated calibration signalthat coarsely adjusts the DC offset level of the I and/or Q componentsof the base-band signal. Having done this, the process repeats at Step162 until an optimal DC offset level is reached. As such, thecalibration determination module selects an initial set of DC offsetvalues for the I and/or Q component. Based on this initial setting, thecalibration determination module increases or decreases thecorresponding DC offsets. If this produces less transmitter DC offset,the calibration determination module fine-tunes these values until anoptimal DC offset is reached. If the initially adjusted values producemore transmitter DC offset, the calibration determination module makes acoarse adjustment in the opposite direction with respect to the initialsettings and then repeats the calibration.

FIG. 8 illustrates a logic diagram that may be performed by thecalibration determination module to determine the calibration signal foradjusting the gain of the I and/or Q components of the base-band signal.The process begins at Step 180 where the calibration determinationmodule provides 1^(st) and 2^(nd) sets of coefficients to the filteringmodule to produce two band-pass filters. The process then proceeds toStep 182 where the calibration determination module adjusts the gain ofthe I and/or Q component of the base-band signal in accordance with thegain correction indication, which is indicated within the calibrationsignal.

The process then proceeds to Step 184 where the calibrationdetermination module produces a new 1^(st) frequency spectrum componentand a new 2^(nd) frequency spectrum component based on the adjusted Iand/or Q components of the base-band signal. The process then proceedsto Step 186 where the calibration determination module determineswhether the new 1^(st) frequency spectrum components represent lesstransmitter imbalance than that represented by the initial frequencyspectrum. If not, the process proceeds to Step 188. At Step 188, thecalibration determination module produces an updated calibration signalto coarsely adjust the gain of the I and/or Q components of thebase-band signal. At this point, the process repeats at Step 182.

When the new 1^(st) frequency spectrum components represent lesstransmitter imbalance than that represented by the 1^(st) frequencyspectrum, the process proceeds to Step 190. At Step 190, the calibrationdetermination module produces an updated calibration signal to fine-tunethe gain of the I and/or Q components of the base-band signal. Theprocess then proceeds to Step 192 where the calibration determinationmodule determines whether an optimal gain setting has been reached. Ifso, the process is complete. If not, the process proceeds to Step 194.At Step 194, the calibration determination module produces updatedfrequency spectrum components based on a further fine-tuning of the gainof the calibration signal. At this point, the process repeats at Step190 until an optimal gain setting is reached.

FIG. 9 illustrates a schematic block diagram of a self-calibratingtransmitter 200 and includes processing module 202 and memory 204. Theprocessing module 202 may be a single processing device or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 204 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 202 implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry. The memory 204stores, and the processing module 202 executes, operational instructionscorresponding to at least some of the steps illustrated in FIG. 10.

FIG. 10 illustrates a logic diagram of a method that may be executed bythe self-calibrating transmitter 200 of FIG. 9. The process begins atStep 210 where the transmitter mixes an I component of a base-bandsignal with an I component of a local oscillation to produce a mixed Isignal. The process then proceeds to Step 212 where the transmittermixes a Q component of the base-band signal with a Q component of thelocal oscillation to produce a mixed Q signal. The process then proceedsto Step 214 where the transmitter sums the mixed I signal with the mixedQ signal to produce a modulated RF signal.

The process then proceeds to Step 216 where the transmitter produces acalibration signal based on an interpretation of the local oscillationand the modulated RF frequency. This may be done as illustrated withrespect to Steps 220-226.

At Step 220, the transmitter mixes the modulated RF signal with thelocal oscillation to produce a base-band representation of the modulatedRF signal. The process then proceeds to Step 222 where the transmitterconverts the base-band representation of the modulated RF signal into adigital base-band signal. The process then proceeds to Step 224 wherethe transmitter filters the digital base-band signal to produce a 1^(st)frequency spectrum component and a 2^(nd) frequency spectrum component.Note that for determining DC offset, the filtering includes low passfiltering and band pass filtering and, when determining gain offset, thefiltering includes complimentary band pass filtering. The process thenproceeds to Step 226 where the transmitter interprets the 1^(st) and2^(nd) frequency spectrum components to produce the calibration signal.The interpretation and subsequent generation of the calibration signalmay be performed as previously illustrated and discussed with referenceto FIGS. 4-6.

Returning to the main flow of the diagram, the process then proceeds toStep 218 where the transmitter calibrates the DC level of the I and/or Qcomponents of the base-band signal and/or calibrates the gain of the Iand/or Q components of the base-band signal based on the calibrationsignal. The corresponding calibration reduces imbalances within thetransmitter thereby enhancing performance of the transmitter and radiosincorporating such transmitters.

FIG. 11 illustrates a schematic block diagram of a radio 230 thatincludes an analog receiver section 236, calibration switch module 232,analog-to-digital converter 66, digital receiver processing module 64,digital transmitter processing module 76, analog transmitter section238, mixing module 254, and a local oscillation module 74. The analogreceiver section 236 receives an inbound RF signal 88 via a low-noiseamplifier 72. The low-noise amplifier 72 amplifies the RF signal 88 andprovides the amplified signal to the down-converting module 70. Thedown-converting module 70 removes the RF carrier from the signal andprovides the down-converted signal to filtering/gain module 68. Thefiltering/gain module 68 filters and/or adjusts the gain of thedown-converted signal to produce an analog low IF signal 244. Note thatthe low IF signal may have a carrier frequency in the range of 0 Hertzto a few megahertz.

The calibration switching module 232 is operably coupled to pass eitherthe analog low IF signal 244 or a base-band representation 256 of the RFsignal 254 to the analog to digital converter 66 based on a switchcontrol signal 246. The calibration switch module 232 will pass theanalog low IF signal 244 during normal operations (i.e., when the radio230 is receiving RF signals) and passes the base-band representation 256of the RF signal 254 when the radio 230 is in a transmitter calibrationmode.

Mixing module 254 produces the base-band representation 256 of the RFsignal 254 by mixing a modulated RF signal 252, which is produced by theanalog transmitter section 238, with an I or Q component of a localoscillation for the transmitter section. The analog transmitter section238 includes the digital to analog converter 8, the filtering/gainmodule 82, the up-converting module 82, and the power amplifier 84. Eachof these modules 78-84 operate as previously discussed to produce themodulated RF signal 252 from a digital baseband signal, which isreceived from the digital transmitter processing module 76.

During normal operations, the digital transmitter processing module 76converts outbound data 94, which is received from the host device, intodigital baseband signals, which may have a carrier frequency of 0 to afew megahertz. As shown, the digital transmitter processing module 76includes a scramble/encode module 101, modulation mapping module 103,and a calibration execution module 102. As previously discussed, thecalibration execution module 102 adjusts gain and/or DC offset of an Icomponent and/or Q component of the digital base-band signal.

Also during normal operations, the analog-to-digital converter 66converts the analog low IF signal 244 into a digital reception formatteddata 90. A digital receiver section 234 within the digital receiverprocessing module 64 processes, in accordance with one of a plurality ofwireless communication standards, the digital reception formatted data90 to produce a 1^(st) baseband digital signal 248, which is provided asinbound data 92 to the host device.

During calibration mode for DC offset, the analog-to-digital converter66 converts the base-band representation 256 of the RF signal 254 intothe digital reception formatted data 90. The digital receiver section234 is configured to include a low pass filter and a band pass filterwhich filter the digital reception formatted data 90 to produce a 2^(nd)base-band digital signal 250. The 2^(nd) baseband digital signal 250includes a 1^(st) frequency spectrum component and a 2^(nd) frequencyspectrum component and is provided to the calibration determinationmodule 240.

The calibration determination module 240 within the digital transmitterprocessing module 76 interprets the 1^(st) and 2^(nd) frequency spectrumcomponents to determine the presence of a DC offset. If a DC offset ispresent, the calibration determination module 240 generates thecalibration signal 242 to reduce and/or eliminate the DC offset.

During calibration mode for gain offset, the analog-to-digital converter66 converts the base-band representation 256 of the RF signal 254 intothe digital reception formatted data 90. The digital receiver section234 is configured to include complimentary band pass filters that filterthe digital reception formatted data 90 to produce a 2^(nd) base-banddigital signal 250. The 2^(nd) baseband digital signal 250 includes a1^(st) frequency spectrum component and a 2^(nd) frequency spectrumcomponent and is provided to the calibration determination module 240.

The calibration determination module 240 interprets these 1^(st) and2^(nd) frequency spectrum components for the presence of a gain offset,or imbalance. If a gain offset exists, the calibration determinationmodule 240 generates the calibration signal 242 to reduce and/oreliminate the gain offset.

The calibration determination module 240 provides the calibrationcontrol signal 242 to the calibration execution module 102, whichadjusts gain and/or DC offset of an I and Q component of the base-banddigital signal 245 based on the calibration control signal 242.Accordingly, the self-calibrating transmitter of FIG. 11 is capable ofself correcting DC offsets, which produces local oscillation leakage ifnot corrected, and is capable of self correcting gain imbalances, whichcauses transmission errors, increased power consumption, etc. if notcorrected.

FIG. 12 illustrates a more detailed schematic block diagram of thecalibration circuitry of radio 230. As illustrated, the calibrationcircuitry includes mixing module 254, digital-to-analog converter 78,the digital receiver section 234, the calibration determination module240 and the calibration execution module 102. The digital receiversection 234 includes a low-pass/band-pass filter 262 and a band-passfilter 264. The calibration determining module 240 includes theinterpreting module 126. The calibration execution module 102 includesthe gain offset module 138, DC offset module 140, gain offset module 142and DC offset module 144. As configured, the components performsimilarly to the circuitry illustrated and discussed with reference toFIGS. 4-6 to produce the calibration signal 242. In this embodiment,however, the calibration circuitry is taking advantage of portions ofthe receiver to facilitate the self calibration of the transmittersection.

FIG. 13 illustrates a schematic block diagram of radio 270 that includesprocessing module 272 and memory 274. The processing module 272 may be asingle processing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 274 may be a single memory device or aplurality of memory devices. Such a memory device may be a read-onlymemory, random access memory, volatile memory, non-volatile memory,static memory, dynamic memory, flash memory, and/or any device thatstores digital information. Note that when the processing module 272implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory storingthe corresponding operational instructions is embedded with thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. The memory 274 stores, and theprocessing module 272 executes, operational instructions correspondingto at least some of the steps illustrated in FIG. 14.

FIG. 14 illustrates a logic diagram of a method for self calibrating atransmitter within the radio 270. The process begins at Step 280 wherethe radio produces a modulated RF signal based on I and Q components ofa base-band signal and I and Q components of a transmitter localoscillation. The process then proceeds to Step 282 where the radio mixesthe modulated RF signal with the I or Q component of the transmitterlocal oscillation to produce a base-band representation of the modulatedRF signal.

The process then proceeds to Step 284 where the radio produces an analoglow IF signal based on a received RF signal and I and Q components of areceived local oscillation. The process then proceeds to Step 286 wherethe radio outputs the analog low IF signal or base-band representationof the modulated RF signal based on a switch control signal. The switchcontrol signal will enable the outputting of the analog low IF signalduring normal mode and the outputting of the base-band representation ofthe modulated RF signal during transmitter calibration mode.

The process then proceeds to Step 288 where a determination is made asto whether the analog low IF signal or base-band representation of theRF signal is being outputted. When the low IF signal is being outputted,the process proceeds to Step 290 where the radio 270 produces a 1^(st)base-band digital signal from the analog low IF signal, which issubsequently provided to the host device as inbound data.

If the base-band representation of the RF signal is being outputted, theprocess proceeds to Step 292 where the radio produces a 2^(nd) base-banddigital signal from the base-band representation of the modulated RFsignal. The process then proceeds to Step 294 where the radio produces acalibration signal based on an interpretation of the 2^(nd) base-banddigital signal. This may be done as previously described with referenceto FIGS. 11 and 12. The process then proceeds to Step 296 where theradio calibrates the DC level of the I and/or Q components of thebase-band signal and/or calibrates the gain of the I and/or Q componentsof the base-band signal based on the calibration signal.

The preceding discussion has presented a self-calibrating transmitterthat corrects for imbalances within the transmitter that, ifuncorrected, would adversely affect the operation of the transmitter byproducing local oscillation leakage, gain imbalances, et cetera. Bycalibrating for these imbalances within the transmitter, a directconversion transmitter may be implemented as an integrated circuit andyield high performances. As one of average skill in the art willappreciate, other embodiments may be derived from the teaching of thepresent invention, without deviating from the scope of the claims.

What is claimed is:
 1. A radio having a self calibrating transmitter,the radio comprises: transmitter section that produces a modulated radiofrequency (RF) signal based on an I component of a baseband signal, an Icomponent of a transmitter local oscillation, a Q component of thebaseband signal, and a Q component of the transmitter local oscillation;mixer operably coupled to mix the modulated RF signal with the I or theQ component of the transmitter local oscillation to produce a basebandrepresentation of the modulated RF signal; analog receiver section thatproduces an analog low intermediate frequency (IF) signal based on areceived RF signal, an I component of a receiver local oscillation, anda Q component of the receiver local oscillation; calibration switchmodule operably coupled to output either the analog low IF signal or thebaseband representation of the modulated RF signal in accordance with aswitch control signal; digital receiver section operably coupled to thecalibration switch module, wherein the digital receiver section producesa first baseband digital signal from the analog low IF signal andproduces a second baseband digital signal from the basebandrepresentation of the modulated RF signal; calibration determinationmodule operably coupled to produce a calibration signal based on aninterpretation of the second baseband digital signal; and calibrationexecution module operably coupled to calibrate at least one of: DC levelof the I component of the baseband signal, DC level of the Q componentof the baseband signal, gain of the I component of the baseband signal,and gain of the Q component of the baseband signal based on thecalibration signal such that the imbalance within the transmittersection is reduced.
 2. The radio of claim 1, wherein the calibrationdetermination module further comprises: processing module; and memoryoperably coupled to the processing module, wherein the memory includesoperational instructions that cause the processing module to generatethe switch control signal when the analog receiver section and digitalreceiver section are available.
 3. The radio of claim 2, wherein thedigital receiver section further comprises: an analog to digitalconverter module operably coupled to produce a digital I signal and adigital Q signal from the baseband representation of the modulated RFsignal; first filter operably coupled to filter the digital I signal toproduce an I component of the second baseband digital signal; and secondfilter operably coupled to filter the digital Q signal to produce a Qcomponent of the second baseband digital signal.
 4. The radio of claim3, wherein the memory further comprises operational instructions thatcause the processing module to: provide a first set of coefficients tothe first and second filters for calibration of DC offset of thetransmitter section; and provide a second set of coefficients to thefirst and second filters for calibration of gain offset of thetransmitter section.
 5. The radio of claim 4, wherein the calibrationexecution module further comprises at least one of: an I component DCoffset module operably coupled to adjust DC level of the I component ofthe baseband signal based on the calibration signal; an I component gainoffset module operably coupled to adjust gain of the I component of thebaseband signal based on the calibration signal; a Q component DC offsetmodule operably coupled to adjust DC level of the Q component of thebaseband signal based on the calibration signal; a Q component gainoffset module operably coupled to adjust gain of the Q component of thebaseband signal based on the calibration signal.
 6. The radio of claim5, wherein the memory further comprises operational instructions that,when the calibration determination module provides the first set ofcoefficients to the first and second filters, cause the processingmodule to: interpret frequency spectrum of the I component of the secondbaseband digital signal to produce a first frequency spectrum component;interpret frequency spectrum of the Q component of the second basebanddigital signal to produce a second frequency spectrum component; andcompare the first and second frequency spectrum components to producethe calibration signal to adjust the DC offset of at least one of the Iand Q components of the baseband signal.
 7. The radio of claim 5,wherein the memory further comprises operational instructions that, whenthe calibration determination module provides the second set ofcoefficients to the first and second filters, cause the processingmodule to: interpret frequency spectrum of the I component of the secondbaseband digital signal to produce a first frequency spectrum component;interpret frequency spectrum of the Q component of the second basebanddigital signal to produce a second frequency spectrum component; andcompare the first and second frequency spectrum components to producethe calibration signal to adjust the gain offset of at least one of theI and Q components of the baseband signal.
 8. A method for transceivingradio frequency (RF) signals including self calibrating transmitting ofthe RF signals, the method comprises: producing a modulated radiofrequency (RF) signal based on an I component of a baseband signal, an Icomponent of a transmitter local oscillation, a Q component of thebaseband signal, and a Q component of the transmitter local oscillation;mixing the modulated RF signal with the I or the Q component of thetransmitter local oscillation to produce a baseband representation ofthe modulated RF signal; producing an analog low intermediate frequency(IF) signal based on a received RF signal, an I component of a receiverlocal oscillation, and a Q component of the receiver local oscillation;outputting the analog low IF signal or the baseband representation ofthe modulated RF signal based on a switch control signal; producing afirst baseband digital signal from the analog low IF signal when theanalog IF signal is outputted; producing a second baseband digitalsignal from the baseband representation of the modulated RF signal whenthe baseband representation of the modulated RF signal is outputted;producing a calibration signal based on an interpretation of the secondbaseband digital signal; and calibrating at least one of: DC level ofthe I component of the baseband signal, DC level of the Q component ofthe baseband signal, gain of the I component of the baseband signal, andgain of the Q component of the baseband signal based on the calibrationsignal.
 9. The method of claim 8 further comprises: generating theswitch control signal when the radio is in a transmitting mode.
 10. Themethod of claim 9, wherein the producing a second baseband digitalsignal from the baseband representation of the modulated RF signalfurther comprises: analog to digital converting the basebandrepresentation of the modulated RF signal into a digital I signal and adigital Q signal from; filtering the digital I signal to produce an Icomponent of the second baseband digital signal; and filtering thedigital Q signal to produce a Q component of the second baseband digitalsignal.
 11. The method of claim 10 further comprises: providing a firstset of coefficients to establish first filtering characteristics for thefiltering of the digital I signal and the digital Q signal forcalibration of DC offset of the transmitter; and providing a second setof coefficients to establish second filtering characteristics for thefiltering of the digital I signal and the digital Q signal forcalibration of gain offset of the transmitter section.
 12. The method ofclaim 11, wherein the producing the calibration signal, when providingthe first set of coefficients, further comprises: interpreting frequencyspectrum of the I component of the second baseband digital signal toproduce a first frequency spectrum component; interpreting frequencyspectrum of the Q component of the second baseband digital signal toproduce a second frequency spectrum component; and comparing the firstand second frequency spectrum components to produce the calibrationsignal to adjust the DC offset of at least one of the I and Q componentsof the baseband signal.
 13. The method of claim 11, wherein theproducing the calibration signal, when providing the second set ofcoefficients, further comprises: interpreting frequency spectrum of theI component of the second baseband digital signal to produce a firstfrequency spectrum component; interpreting frequency spectrum of the Qcomponent of the second baseband digital signal to produce a secondfrequency spectrum component; and comparing the first and secondfrequency spectrum components to produce the calibration signal toadjust the gain offset of at least one of the I and Q components of thebaseband signal.
 14. An apparatus for transceiving radio frequency (RF)signals including self calibrating transmitting of the RF signals, theapparatus comprises: processing module; and memory operably coupled tothe processing module, wherein the memory includes operationalinstructions that cause the processing module to: produce a modulatedradio frequency (RF) signal based on an I component of a basebandsignal, an I component of a transmitter local oscillation, a Q componentof the baseband signal, and a Q component of the transmitter localoscillation; mix the modulated RF signal with the I or the Q componentof the transmitter local oscillation to produce a basebandrepresentation of the modulated RF signal; produce an analog lowintermediate frequency (IF) signal based on a received RF signal, an Icomponent of a receiver local oscillation, and a Q component of thereceiver local oscillation; output the analog low IF signal or thebaseband representation of the modulated RF signal based on a switchcontrol signal; produce a first baseband digital signal from the analoglow IF signal when the analog IF signal is outputted; produce a secondbaseband digital signal from the baseband representation of themodulated RF signal when the baseband representation of the modulated RFsignal is outputted; produce a calibration signal based on aninterpretation of the second baseband digital signal; and calibrate atleast one of: DC level of the I component of the baseband signal, DClevel of the Q component of the baseband signal, gain of the I componentof the baseband signal, and gain of the Q component of the basebandsignal based on the calibration signal.
 15. The apparatus of claim 14,wherein the memory further comprises operational instructions that causethe processing module to: generate the switch control signal when theradio is in a transmitting mode.
 16. The apparatus of claim 15, whereinthe memory further comprises operational instructions that cause theprocessing module to produce the second baseband digital signal from thebaseband representation of the modulated RF signal by: analog to digitalconverting the baseband representation of the modulated RF signal into adigital I signal and a digital Q signal from; filtering the digital Isignal to produce an I component of the second baseband digital signal;and filtering the digital Q signal to produce a Q component of thesecond baseband digital signal.
 17. The apparatus of claim 16, whereinthe memory further comprises operational instructions that cause theprocessing module to: provide a first set of coefficients to establishfirst filtering characteristics for the filtering of the digital Isignal and the digital Q signal for calibration of DC offset of thetransmitter; and provide a second set of coefficients to establishsecond filtering characteristics for the filtering of the digital Isignal and the digital Q signal for calibration of gain offset of thetransmitter section.
 18. The apparatus of claim 17, wherein the memoryfurther comprises operational instructions that cause the processingmodule to produce the calibration signal, when providing the first setof coefficients, by: interpreting frequency spectrum of the I componentof the second baseband digital signal to produce a first frequencyspectrum component; interpreting frequency spectrum of the Q componentof the second baseband digital signal to produce a second frequencyspectrum component; and comparing the first and second frequencyspectrum components to produce the calibration signal to adjust the DCoffset of at least one of the I and Q components of the baseband signal.19. The apparatus of claim 17, wherein the memory further comprisesoperational instructions that cause the processing module to produce thecalibration signal, when providing the second set of coefficients, by:interpreting frequency spectrum of the I component of the secondbaseband digital signal to produce a first frequency spectrum component;interpreting frequency spectrum of the Q component of the secondbaseband digital signal to produce a second frequency spectrumcomponent; and comparing the first and second frequency spectrumcomponents to produce the calibration signal to adjust the gain offsetof at least one of the I and Q components of the baseband signal.